1. Field of the Invention
The present invention relates to a filter for trapping foreign matter, comprising an inflow chamber into which a fluid flows, an outflow chamber from which flows the fluid that has flown into the inflow chamber, and a filter element partitioning the two chambers.
2. Description of the Related Art
If impurities (foreign matter) such as dirt, carbon powder, metal powder (iron powder) are admixed to a hydraulic oil (working oil) in hydraulic apparatuses (hydraulic equipment), then sliding portions of hydraulic pumps, hydraulic motors, and hydraulic cylinders, that is, contact zones of movable mechanisms and fixed mechanisms in those components are subjected to wear, or movement of the movable mechanisms is inhibited. If a hydraulic apparatus is continuously used in such a state, the operation efficiency of the hydraulic apparatus is decreased and the quantity of the foreign matter in the hydraulic apparatus increases with the extension of the use interval of the hydraulic apparatus, eventually damaging the apparatus such as the hydraulic pump.
Accordingly, a variety of suggestions have been made with the object of improving the technology of removing (filtering) foreign matter from the hydraulic oil in the filters that together with aforementioned hydraulic pumps or the like constitute hydraulic apparatuses. According to one of the suggestions, there is provided a configuration (filter element and filtration apparatus) in which a spacer is provided between the opposing filters, the deformation of the filter by the pressure acting upon the filter surface during backwashing is prevented, the impurities that were deposited on the opposing filter surfaces are prevented from coming into contact with each other, a flow path for the fluid containing the impurities that were separated by backwashing is maintained, and the impurities that were separated from the filter can be easily discarded (for example, see Japanese Patent Application Laid-open No. H10-258221).
Because a constant relationship exists between the quantity of foreign matter that is admixed to a hydraulic oil and the degree of wear and damage of the hydraulic pump or hydraulic motor, if the quantity of foreign matter can be assessed, then the degree of wear and damage of the hydraulic pump or the like can be established. The quantity of foreign matter can be assessed by measuring the differential pressure (pressure loss) in the filter element generated owing to the entrapment of the foreign matter by the filtration element.
The above-described conventional technology was suggested with the object of increasing the cost efficiency by extending the interval representing the service live of the filter element and also increasing the cost efficiency by reducing the number of filter elements in a single filtration apparatus by using filter elements with high capacity of trapping foreign matter. This technology involved the so-called surface filtration by which the hydraulic oil is filtered by trapping foreign matter with the surface of the filter element and was not, in the first place, suggested with the object of trapping foreign matter admixed to hydraulic oil. For this reason, in the aforementioned conventional technology, the filtration apparatuses are not constructed for reliably trapping foreign matter that flows together with hydraulic oil into the filtration apparatus, and the foreign matter that was rejected by the filtration element and was not trapped accumulates on the bottom of the filtration apparatus.
Accordingly, the problem associated with the filtration apparatuses of the conventional technology was that even if the differential pressure in the filter element that is caused by the entrapment of foreign matter in the filter element was measured, the quantity of the foreign matter that has been admixed to hydraulic oil could not be assessed accurately. As a result, the damage of hydraulic pumps or the like was difficult to prevent in advance by implementing the necessary maintenance before the wear or damage state of the hydraulic pump or the like becomes severe.